High molecular weight ("HMW") kininogen and low molecular weight ("LMW") kininogen are known kininogens in blood plasma. Both of these kininogens carry a kinin protein moiety in their polypeptide chain. This region is in turn bridged by a disulfide bond so as to form a looped structure. Upon liberation of the kinin protein (through the operation of an enzyme known as kallikrein) dimer variants of these compounds are formed. In the HMW variant, liberation of kinin results in a disulfide bonded dimer of an amino-terminal H-chain and a carboxyl L-chain. See generally Y. Takagaki et al. 260 J. Biol. Chem. 8601-8609 (1985).
The H-chains of HMW and LMW kininogens are identical. However, the L-chains are different. The L-chain of the HMW kininogen is larger than the L-chain of the LMW kininogen, and is known to contain a region rich in histidine, a region rich in basic residues, and a region rich in acidic acid residues. It is also known that two other plasma proteins (pre-kallikrein and blood coagulation Factor XI) bind to HMW kininogen via the acidic region in the L-chain (J. Tait et al., 261 J. Biol. Chem. 15396-15401 (1986)); and that binding of HMW kininogen to negatively charged surfaces is enhanced by cleavage to form the two chain kinin free form (C. Scott et al., 73 J. Clin. Invest. 954-962 (1984)).
The mechanism of cleavage is thought to involve binding of HMW kininogen and pre-kallikrein (and HMW kininogen Factor XI complexes) to surfaces alongside blood coagulation Factor XII. This is referred to as "contact activation". Reciprocal activation of the surface generates the enzyme kallikrein, which then in turn cleaves the HMW kininogen to yield a polypeptide previously named "kinin-free HMW kininogen" (herein referred to as "passifin"). See also L. Vroman et al., 55 Blood 156-159 (1980) and A. Schmaier et al., 33 Thromb. Res. 51-67 (1983).
While considerable research has been run on the function and structure of kinin-free HMW kininogen, there has to date been no suggestion in the art that a conduit or other surface normally exposed to blood and/or animal cells could first be exposed to an exogenous (from outside the host) supply of a proteinaceous material present in kinin-free HMW kininogen to reduce the tendency of the blood to block the conduit or surface.